Neurosurgery sometimes involves inserting an electrode such as a recording or stimulating electrode (for recording brain signals or providing stimulating pulses), or other instrument (for example, a catheter for fluid aspiration or drug infusion) through a burr hole or other entry portal into a subject's brain towards a target region of the brain. The present inventors have recognized an unmet need for normalizing stage devices, tools, and methods that provide a known distance between a stage and a target, such as to reduce or avoid physician and technician calculations and equipment adjustments.